1. Field of the Invention
The present invention relates to a rotating control circuit, in particular to a rotating control circuit for a construction machine.
2. Description of the Related Art
A hydraulic excavator, especially a hydraulic excavator with short tail swing radius has a small inertia force of upperrotating body at the time of stopping a rotating operation. For this reason, when the rotating operation is abruptly stopped, a machine body of the excavator may be flapped. Furthermore, for the same reason, the machine body may also be flapped at the time of starting the rotation.
It is an object of the present invention to provide a rotating control circuit which can avoid a flapping of a machine body at the time of stopping the rotation of upper rotating body of construction machine and the like.
A construction machine according to the present invention has a rotating control circuit for a working machine provided with a rotating body, wherein the rotating control circuit comprises:
a hydraulic motor adapted to be rotationally driven by supplying hydraulic fluid from hydraulic fluid source by way of a direction control valve; operating means adapted to switch the direction control valve between a rotating position and a neutral position; a bypath line connected between both hydraulic lines of the hydraulic motor; a communicating valve having switch positions comprising a first position for closing the bypath line and a second position for opening the bypath line; and a controller adapted to control the switch positions of the communicating valve. The controller is adapted to set the communicating valve to the first position at the rotating position or the neutral position and to set the communicating valve to the second position when the communicating valve is switched to a position different from the first position, as well as to allow the hydraulic fluid of deceleration side at the time of stopping the rotation, and the hydraulic fluid of acceleration side at the time of starting the rotation, to be released by a predetermined time.
The afore-mentioned xe2x80x9ca position different from the first positionxe2x80x9d is illustrated by two cases as follows:
First is the case where said controller is adapted to set an escape valve or a bypath valve to a closed position at the time when the operating means is operated for rotation, and to set the bypath valve to an open position at the time when the operating means is returned to the neutral position, thereby allowing the hydraulic fluid of deceleration side to be released by the predetermined time.
In this case, a reverse motion of motor torque changed from acceleration to deceleration is delayed at the time of stopping the rotating operation. Thereby, an abrupt stopping will not be caused in the construction machine, in particular even if the inertia force of upper rotating body is small as in the hydraulic excavator with short tail swing radius, and there will be no flapping of a machine body of the excavator.
Therefore, an operator does not feel lurch with his (her) body at the time of stopping the rotating operation and a comfortable maneuverability can be attained.
Next is the case where said controller is adapted to set the communicating valve to the first position at the time when said operating means is in the neutral position and to set the communicating valve to the second position at the time when the rotating operation is started, thereby allowing the hydraulic fluid of acceleration side to be released by the predetermined time.
In this case, an acceleration of motor torque is delayed at the time of starting the rotation. Therefore, even if the inertia force of upper rotating body is small as in the hydraulic excavator with short tail swing radius, the abrupt rotation will not be caused. As a result, there will be no rocking of hull. Thereby, the operator does not feel large rocking with his (her) body at the time of starting the rotation, whereby a comfortable maneuverability can be attained.